In recent years in the semiconductor industry, the integration level of ICs has rapidly increased. It has increased from 4M to 16M and is now proceeding to the 64M level.
In light of the above circumstances, demand for a wafer having a higher-quality surface from which ICs are formed has increased. In order to increase the integration level of ICs, aside from improvement of the chemical and electrical properties of the wafer, reduction of the minimum width allocated for devices to be formed on the wafer is increasingly demanded. Now, 0.35 microns is requested, as compared to 0.5 microns in the past. Moreover, the size of the wafer has rapidly increased, followed by rapid reduction of cost per bit. With the increase in the size of the wafer, the size of machines for processing the wafer has increased. For example, in the polishing process for mirror-finishing the wafer surface, a polishing machine with a base plate having a diameter of about 42 inches is used for 5'-diameter wafers, while a polishing machine with a base plate having a diameter as large as 59 inches is used to polish 8'-diameter wafers. In general, the polishing of wafers is performed by causing friction with a polishing cloth in the presence of a polishing slurry, while retaining the polishing cloth on a lower base plate of a polishing machine and the wafer to be processed on an upper base plate.
The size of the polishing cloth should therefore be the same as that of the lower base plate of the polishing machine. Specifically, a polishing cloth with a diameter of about 42 inches is generally used for polishing 5'-diameter wafers, while a polishing cloth with a diameter of 59 inches is used for polishing 8'-diameter wafers.
In general, the polishing cloth is secured to the base plate of the polishing machine with a high-performance double-sided adhesive tape; that is, a tape having adhesive layers on the both sides. Such an adhesive tape is attached to the back surface of the polishing cloth. In this securing method, however, such an adhesive layer formed on the back surface of the polishing cloth is adhered to the base plate so firmly that a tack strength as large as about 2 to 3 kg/inch width is exhibited when the polishing cloth attached to the base plate is intended to be detached in a general manner. This means that a force of 156 kg at minimum is required to detach the polishing cloth from the base plate with a diameter of 42 inches, while a force of 180 kg at minimum is required when a base plate with a diameter of 59 inches is used. Thus, it takes an extraordinarily large amount of labor to exchange a used polishing cloth with a new one.
Thus, the invention described herein makes possible the advantages of (1) providing a polishing cloth which adheres to a base plate of a polishing machine firmly, stably, and precisely when a wafer is polished and is easily detached from the base plate when intended to be detached, (2) providing a method for attaching/detaching such a polishing cloth to/from the base plate of the polishing machine, (3) providing a polishing cloth which, when being exchanged or replaced, can be easily peeled off a base plate of a polishing machine by simply cooling the base plate and an adhesive layer of the polishing cloth, and (4) providing a method for attaching/detaching such a polishing cloth to/from the base plate of the polishing machine.